Failure to thrive (FTT) is a disorder of physical growth in which children of previously normal weight fall below standards for age. Although its etiology is unknown, studies indicate that children with FTT and their mothers are subject to a variety of psychosocial stressors. We propose to study FTT as a stress response syndrome, using adrenocortical activity during feeding and play as a biological indicator of the stress response. There are two components of the proposed project: First, a study of social, behavioral, emotional, and adrenocortical functioning in 150 9- to 24-month-old FTTs and 150 normally-growing children from the same age range, and their mothers. For mothers and children, measures will be obtained for (a) environmental factors (demographics, socioeconomic status, life stress, social support, and marital satisfaction); (b) individual maternal and child factors (child emotional expression and temperament; maternal psychiatric disorders); (c) interactional factors (emotional behavior in play and feeding, and attachment); and (d) adrenocortical activity (salivary cortisol). Second, a longitudinal study of individual differences in growth outcome in the FTT group, in which all children with FTT will be followed for one year after intake. At three-month intervals, children will be examined, anthropometric data updated, and parents interviewed about the child's diet. At 6 and 12 months after intake, the environmental, individual, and interactional measures will be repeated. Analyses will focus on (1) group differences between FTTs and normals on measures of behavior, emotional expression, and patterns of adrenocortical activity; (2) associations among behavior, maternal psychopathology, infant attachment and adrenocortical activity; and (3) individual differences among FTTs in the environmental, individual, interactional, and adrenocortical activity, as predictors of growth outcome.